The present invention relates to an ultrasound imaging apparatus using a digital beam focusing scheme. More particularly, the present invention relates to a receive beamforming apparatus for processing a plurality of scan lines or beams. It includes delay elements structured into multiple stages.
As well known in the art, an ultrasound imaging system using an array of transducers includes a phased, convex or linear array of multiple transducers. Such a system includes multiple channels, each channel having a transmitter and a receiver connected to a corresponding transducer. The transmitter applies ultrasound pulses to an object such as one in a human body. To focus the transmitted ultrasound energy to a certain point in the object, sequential time delays are applied to the pulses. The amount of delay for each pulse is determined in a way that the transmitted pulses reach a target point simultaneously. These pulses pass through diverse materials/medium before focused on the object and the reflected pulses pass through the materials again, back to the array.
The ultrasound energy reflected from the object reaches each of the array elements at different times because the distances from the object to the array elements are different from each other. At a receive beamformer, the receive signals from the array elements are amplified; a time delay is applied to each of the amplified signals; and the delayed signals are summed. The amount of delay for each delay element is determined such that the signals are focused at a point in a receive scan line or beam. The amount of delay for each element is changed constantly so that the focusing point moves in a radial direction.
To form an ultrasound image, a desired region in a body should be scanned with transmitted pulses, and a received signal/data is processed to provide the image of the desired region. To provide a high quality image, it is essential to increase the frame rate. The frame rate is determined by the number of scanlines used, the frequency of ultrasound pulses and the depth of a region whose image is to be formed. To increase the frame rate, a multi-beam focusing technique has been used where multiple scanlines or beams, rather than one scan line, are formed after transmitting ultrasound pulses.
In a multi-beam-forming apparatus, a different amount of delay should be applied for each beam and per channel, thus increasing the complexity of a system. Especially, the capacity of a memory device used as the delay elements is increased. In a conventional beamformer, the capacity of a needed memory device is proportional to the number of channels, the maximum amount of delay and the number of beams formed after one transmission. For example, for a system with 64 channels, quadruple beams, a maximum delay of 1000 system clock cycles, and 10 bit data length, 64xc3x974xc3x971000xc3x9710 bits of memory space is necessary.
Therefore, it is an objective of the present invention to provide a novel structure of a beamformer which can decreases the size of the delay memory.
It is another objective of the present invention to provide a beamformer which produce data for multiple receive scanlines in a time multiplexed manner.
In accordance with one aspect of the present invention, there is provided an ultrasound receive beamforming apparatus for processing signals received from an array of transducers, comprising: a plurality of beamforming devices, each device applying delays to data samples of M channels provided from M transducers for forming N receive beams and adding delayed data samples of M channels to provide N intermediate outputs, N and M being positive integers less than the number of transducers in the array; adders for summing the intermediate outputs from said plurality of beamforming devices, to provide data representing the N receive beams, wherein each of said beamforming devices includes: a predetermined number of per-channel delay elements which provide first delays to the data samples of M channels, to provide delayed data per each channel and per each receive beam, first adders for adding the delayed data of not less than 2 channels provided from the per-channel delay elements, and multi-channel delay elements which provide second delays to the outputs of the first adders.